Water addition to internal combustion systems has been of passing interest for varied reasons since the 1930's. As early as 1935 the use of water injection for suppression of knock in spark ignition engines was investigated. Generally a number of techniques for adding water to fuel prior to combustion, for a multitude of purposes, have been investigated since the early 1920's.
Some of the advantages of water addition to fuel results from a decrease in the combustion temperatures. These temperature reductions result in the suppression of spark-knock and preignition in the engine as well as the reduction of exhaust NO.sub.x concentrations and smoke, and lower fuel consumption.
During the Second World War water injection was employed to maintain the mechanical integrity of aircraft engines during high power output. In the 1970's interest in emulsified fuels for use in diesel engines was renewed because of the possibility of reducing the pollutants emitted by automobiles.
Emulsified fuels are even more attractive today since not only do they reduce the emission of pollutants but even offer the possibility of increased power output and decreased fuel consumption. Generally, there are three ways in which water is introduced into the cylinder of an internal combustion engine. First is the fumigation or carburetion of the water into the intake manifold which results in a slight decrease in NO.sub.x emissions and pre-ignition combustion suppression. Such systems are low in cost, have minimal installation problems and may be easily retro-fitted to existing engines. The primary problem with fumigation is that it is not effective in increasing efficiencies or reducing fuel consumption.
An alternative approach is the direct injection of water into the cylinder of the engine. This results in a substantial decrease in NO.sub.x production, suppression of knock and slight soot reduction. Nevertheless, such a system suffers from a number of substantial disadvantages, namely, high installation costs, high initial equipment costs (this technique requires a redesign of the engine) and little increase in efficiency.
The third approach to the problem of water injection is the fueling of an engine with a fuel/water emulsion. This results in a substantial decrease in NO.sub.x emission, soot production, CO.sub.x emissions and odor. Moreover, engines fueled with emulsions exhibit an increase in output power and thermal efficiency. These advantages plus the possibility of easily and economically retrofitting existing equipment evidence the excellent possibilities for the practical use of emulsified fuel systems.
In spite of the theoretical potential of emulsified fuel systems, practical considerations have resulted in some questions as to the feasibility of commercially implementing such systems in the proximate future. In a recent work on emulsified fuel published by the A.S.M.E. (Paper No. 78224) entitled "Experimental Reduction of NO.sub.x Smoke and BSFC in a Diesel Engine Using Uniquely Produced Water (0-80%) to Fuel Emulsion" considers the problems of practical applications to be as follows:
1. Control of the water/oil emulsion under varying engine load conditions.
2. Durability of the engine and the water injection equipment.
3. Water freezing in the system, especially in colder climates.
4. Necessity of having a water tank to supply water for the emulsion.
5. Deterioration of the lubricating oil in the engine.
Thus, while preparing a fuel/water emulsion for combustion in a diesel engine appears a practical possibility, the development of a simple and reliable method for producing the emulsion and feeding it to the engine involves many considerations. One technique is to produce the emulsion with mechanical equipment, storing the emulsion using an emulsifying agent to maintain the stability of the emulsion. However, this technique has a number of drawbacks. Specifically, the emulsion can only be maintained in storage for a limited period of time before it begins to separate. In addition, pollutants produced by the burning of the emulsifying agent during combustion have proven to be very harmful, thereby defeating one of the main purposes of the using an emulsion.
A second approach to the problem of emulsion production is mechanical emulsification of the fuel just prior to injection into the cylinder. This way the problems involved with storing the emulsion and the disadvantages of using an emulsifying agent are eliminated. The major difficulty with this approach is controlling the fuel/water under a variety of engine conditions. This problem is especially acute in view of the complexities of the operation of a diesel engine and the variation of its parameters under actual operating contitions. Thus, most practical systems have gone in the direction of basic modification of engine design or the like.